The invention relates to a friction ring for reel shafts, having on its inner periphery a friction surface for frictional engagement with the reel shaft, and on its outer periphery a plurality of radially projecting leaf springs that are inclined relative to the radial direction in a uniform direction of rotation, each leaf spring having a base portion held in a slot of the friction ring.
Such friction rings are used in particular in longitudinal cutting and reeling apparatus in which a web of a material that is capable of being reeled is divided into a plurality of narrow strips in longitudinal direction and each strip is then wound onto a respective hub. Typically, a plurality of hubs are mounted on a common reel shaft. The friction rings serve for transmitting the torque of the reel shaft frictionally onto the hubs, so that differences in reeling speed that may be caused by minor differences in the diameters of the coils formed on the different hubs may be compensated by slippage of the friction rings and hence the hubs on the reel shaft. The inclination of the leaf springs provides the possibility to thrust the hubs that are in most cases formed by cardboard sleeves onto one or more friction rings in a screw-like rotary movement. During the reeling operation the inclination in conjunction with the transmitted torque assures that the distal ends of the leaf springs are self-lockingly clawed in the inner peripheral surface of the cardboard sleeves so that tolerances in the diameters of the hubs can be compensated and each hub is reliably driven by the associated friction rings.
The friction rings should have axial dimensions as small as possible so that even narrow strips may be wound onto correspondingly narrow hubs. When the hubs have a larger width, two or more friction rings may be provided per hub.
DE 28 56 066 A1 discloses a friction ring of the type mentioned above wherein the leaf springs and the corresponding slots in the friction ring are straight.
EP 1 316 524 B1 discloses a friction ring wherein the leaf springs are replaced by drop-shaped clamping bodies that are pivotally supported in corresponding recesses of the friction ring, so that their outwardly projecting tips may be clawed into the hub. The range of pivotal movement of each clamping body is limited by the walls of the recess.